Author Topic: Ohrndorf 5 Cylinder Radial  (Read 7360 times)

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #135 on: November 13, 2021, 11:14:40 PM »
Some trial & error futzing, eventually I arrived at combination where the liners could be re-inserted & the bores were undersized in the 0.0005 – 0.0010” range.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #136 on: November 13, 2021, 11:15:31 PM »
So once again, the liner bores were re-lapped to target ID, this time as a mated assembly. I will now call these good. I had the bright idea to submerge the assemblies in my ultrasonic cleaner again to remove trace lapping compound. But very shortly thereafter I noticed some corrosion stains starting to form on the liner surface, so I immediately pulled them out. Swabbing & rinsing with mineral spirits is a better way to go. Then a light coat of oil for storage.

Next engine I would leave the liner bores unfinished (undersized) at the boring bar stage. Some of the interference surface conditioning could probably be minimized, particularly if there was no need to pull & replace the liner. The cylinder assembly would now have to be jigged so that the grinding / lapping / honing operation could proceeded on the mated surfaces.

Offline Roger B

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Re: Ohrndorf 5 Cylinder Radial
« Reply #137 on: November 14, 2021, 07:43:58 AM »
That was quite a journey  :ThumbsUp:  :praise2:  :wine1: I do like Acrolaps  :)  :)
Best regards

Roger

Offline Admiral_dk

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Re: Ohrndorf 5 Cylinder Radial
« Reply #138 on: November 14, 2021, 11:42:07 AM »
Woa - that part of the journey ended up being a lot more winding than anticipated ....

So I hope that you are really satisfied with the result !!!
I think they all look good and should work very nicely on the finished engine.

Per

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #139 on: November 14, 2021, 06:15:56 PM »
A question came up on the other forum, so pasting reply as further elaboration if my saga verbiage was not quite clear.

I don't think there is an advantage to excessive interference, in fact several potential disadvantages. For example, in my case where the cylinder shape is tapered & thicker wall near the top can contribute to different shrink force on upper vs. lower liner. Pretty much every RC engine I have disassembled requires oven heat to install & remove the liner, even when brand new. My initial heat testing was based on a separate spare test cylinder which was the original design, not my subsequent modified design. But I think either reamed ID surfaces were not as consistent, or possibly they stress relieved a bit. In this kind of application, a half thou one way or another seems to make a big difference. My longwinded story was just to say in hindsight I would not bother grinding & lapping the liner bore until mated to cylinder & completely stabilized. Unless you have good shop methods to very tightly control both OD & ID dimensions & finishes. Jung provides these instructions in his 5-cylinder engine which is probably not far off how mine ended up after lapping the cylinder ID (0.02mm = 0.0008”).

To ensure optimum heat transfer, the cylinder liners must be shrunk into the cylinders. The inner diameter of the cylinder is about 0.02 mm smaller than the respective outer diameter of the liners to unscrew. After uniform heating of the aluminum cylinder by means of gas burner or hot plate (to about 200 ° C), the cold liners are inserted into the cylinder.